1. Field of the Invention
This invention relates to the use of certain acetonitrile derivatives as activators for peroxygen compounds, more particularly inorganic peroxygen compounds, for bleaching colored soil on dishes and to dishwashing detergents containing such activators.
2. Discussion of Related Art
Inorganic peroxygen compounds, more particularly hydrogen peroxide, and solid peroxygen compounds which dissolve in water with release of hydrogen peroxide, such as sodium perborate and sodium carbonate perhydrate, have long been used as oxidizing agents for disinfecting and bleaching purposes. The oxidizing effect of these substances in dilute solutions depends to a large extent on the temperature. For example, with H.sub.2 O.sub.2 or perborate in alkaline bleaching liquors, soiled textiles are only bleached sufficiently quickly at temperatures above about 80.degree. C. At lower temperatures, the oxidizing effect of the inorganic peroxygen compounds can be improved by the addition of so-called bleach activators, for which numerous proposals, above all from the classes of N- or O-acyl compounds, for example polyacylated alkylenediamines, more especially tetraacetyl ethylenediamine, acylated glycolurils, more especially tetraacetyl glycoluril, N-acylated hydantoins, hydrazides, triazoles, hydrotriazines, urazoles, diketopiperazines, sulfuryl amides and cyanurates, also carboxylic anhydrides, more especially phthalic anhydride, carboxylic acid esters, more especially sodium nonanoyloxy benzenesulfonate, sodium isononanoyloxy benzenesulfonate, and acylated sugar derivatives, such as pentaacetyl glucose, have become known in the literature. By adding these substances, the bleaching effect of aqueous peroxide liquors can be increased to such an extent that substantially the same effects are obtained at temperatures of only around 60.degree. C. as are obtained with the peroxide liquor alone at 95.degree. C.
In the search to find energy-saving washing and bleaching processes, application temperatures well below 60.degree. C., more particularly below 45.degree. C. down to the temperature of cold water, have acquired increasing significance in recent years.
At these low temperatures, there is generally a discernible reduction in the effect of the hitherto known activator compounds. Accordingly, there has been no shortage of attempts to develop more effective activators for this temperature range, but so far to no real avail.
Another problem which particularly affects machine dishwashing detergents is the need to incorporate corrosion inhibitors for table silver in such detergents, particularly where the detergents contain the oxygen-based bleaching or oxidizing agents which have recently become more widespread. During the dishwashing process, silver is capable of reacting with sulfur-containing substances dissolved or dispersed in the wash liquor, because food residues, including inter alia mustard, peas, egg and other sulfur-containing compounds, such as mercaptoamino acids, are introduced into the wash liquor in the cleaning of dishes in domestic dishwashing machines. The far higher temperatures prevailing during machine dishwashing and the longer contact times with the sulfur-containing food remains also promote the tarnishing of silver by comparison with manual dishwashing. In addition, the silver surface is completely degreased by the intensive cleaning process in the dishwashing machine and, as a result, becomes more sensitive to chemical influences.
The problem of tarnishing becomes acute in particular when active oxygen compounds, for example sodium perborate or sodium percarbonate, are used alternatively to the active chlorine compounds which oxidatively "deactivate" the sulfur-containing substances in order to eliminate bleachable soils, such as for example tea stains/tea films, coffee residues, dyes from vegetables, lipstick residues and the like.
Active oxygen bleaching agents of the type in question are generally used together with bleach activators, above all in modern low-alkali machine dishwashing detergents of the new generation. These detergents generally consist of the following functional components: builder component (complexing agent/dispersant), alkali carrier, bleaching system (combination of bleaching agent and bleach activator), enzyme and surfactant. Under the dishwashing conditions prevailing where detergents such as these are used, not only sulfidic coatings, but also oxidic coatings are generally formed on the silver surfaces--where silver is present--through the oxidizing effect of the peroxides formed as intermediates or the active oxygen.
The problem addressed by the present invention was to improve the oxidizing and bleaching effect of peroxygen compounds, more especially inorganic peroxygen compounds, at low temperatures below 80.degree. C. and, more particularly, at temperatures in the range from about 15.degree. C. to 55.degree. C.
It has now been found that certain acetonitrile derivatives which carry a quaternary nitrogen substituent have a distinct bleach-boosting effect on colored stains on crockery, such as saucers and plates, or cutlery when used together with peroxidic bleaching agents.